With the operation of DC transmission projects increases, the DC magnetic biasing phenomena occurs sometimes in surrounding substations, which will harm the safe operation of power grid. This paper used PSCAD software for power system to build the model of DC power grid. Taking 500 kV Hanshan substation as an example, the DC power flow was calculated, when the neutral point of main transformer used low resistance or blocking capacitor. Finally, the suppression measures were adopted to improve the ability of stable operation for transformer substations.